1. Field of the Invention
The present invention relates to a thermal imaging paper and a method of making a thermal imaging paper. In particular, the present invention relates to an thermal imaging laminate structure that includes a thermal imaging layer, an integrated circuit and antenna device, and a cushioning layer.
2. Description of the Background Art
Memory tags or labels for storing and retrieving data in the background art often employ a laminated circuit substrate positioned between a face sheet and a release liner. The memory devices for storing and retrieving data are well known in the related art, and include radio frequency (“RF”) tags that are readily available from a number of commercial manufacturers, including Texas Instruments and Phillips.
The face sheet provides a protective layer over one surface of the circuit substrate, thereby protecting the antenna and the electronic structure. A pressure sensitive adhesive may cover a second surface of the circuit substrate to readily affix the memory device to an item or container. The release liner provides a selectively removable layer over the pressure sensitive adhesive, which a user removes before applying the memory tag to an item or container.
The memory device of the background art may include a circuit substrate having an electronic structure such as an integrated circuit, and electrical connections such as traces and pads. For RF tag memory devices, an antenna is coupled to one or more pads of the circuit substrate. The electronic structure typically includes a memory portion and a logic portion. The logic portion controls the reading, writing, or manipulating of data in the memory portion. The logic portion further couples the memory portion to the antenna to form a transmitter, receiver, or transceiver for reading or writing data to or from the RF tag. Thus, for example, an RF tag may receive and transmit RF signals to write data to the memory and to read data from the memory.
U.S. Pat. No. 6,147,604 to Wiklof et al., the entire contents of which are hereby incorporated by reference, further describes the background art relating to wireless memory devices having a circuit substrate positioned within a laminate structure. The device described in the Wiklof et al. patent specifically provides a memory device having a substrate, an antenna formed on a first surface of the substrate, an electronic structure carried by the substrate and coupled to the antenna, a selectively deformable intermediate layer covering the first surface, the antenna and the electronic structure, and an adhesive layer covering the intermediate layer. In addition, the wireless memory device of the Wiklof et al. patent describes the use of a substrate, e.g., a flexible sheet type material having very low conductivity and preferably heat-resistant such as sheet plastic. The intermediate layer may take the form of a foam material, a selectively pressurizable and deformable envelope or other elastomeric material.
The intermediate layer is deformable for selectively positioning the antenna with respect to the adhesive layer, and thereby positioning the antenna with respect to an item or container to which the memory device is secured. The intermediate layer may be compressed, creating a relatively low profile for permitting printing on the memory device. In use, the intermediate layer may be in an uncompressed state, thereby spacing the antenna relatively from the adhesive layer and consequently spacing the antenna from the item or package to which the memory device is secured.
The device of the Wiklof et al. patent is aimed at specifically overcoming a prior art problem relating to the positioning of the wireless memory device's electrical components. If the antenna in an RF tag is too close to the device to which it is installed, unfavorable interference with wireless communications may be experienced, especially when the underlying container is made of metal.
With improvements in wireless memory devices, the necessity of providing a selectively deformable intermediate layer in a laminate structure is not essential for all applications. In addition, the present inventor has determined that the a thermal imaging laminate structure having a memory device and not requiring a selectively deformable intermediate layer can be cost effectively and advantageously employed in a variety of thermal imaging applications. In contrast to the heat resistant substrate of the background art devices such as that described in the Wiklof et al. patent, the present inventor has determined that a heat activated layer can be effectively utilized in conjunction with thermal imaging applications.